1. Field of the Invention
The present invention relates to improved vacuum electron device electrodes and other microwave components manufactured from highly oriented pyrolytic graphite (HOPG).
2. Description of Related Art
The components used in the manufacture and assembly of vacuum electron devices, such as RF output vanes, RF straps, traveling wave tube (TWT) slow wave circuits and output lines, Linear Beam cavity drift tubes, meander lines, and thyratron electrodes, among others, are known in the art. These components are very typically manufactured from copper because of its good thermal conductivity, relative low cost, and machineability. For higher peak power densities, the copper is often cladded with tungsten or molybdenum.
For example, FIGS. 1a through 1c depict an internally cooled copper vane 102 from an AEGIS-style microwave amplifier, typical of the prior art, that failed due to cavitation erosion. As evident from the figures, the cooling channel 104 in the vane 102 shows cavitation damage in region 106 and pinhole breakthrough that caused failure of this device.
Up to now, suitable alternatives to copper and copper clad for manufacturing microwave electrodes have not been known or been readily available. While certain materials are known to have high thermal conductivity and other desirable properties, they have not been considered for use as microwave components because of the perceived difficulty of machining, brazing, and otherwise adapting them for microwave applications. For example, it is known that highly-oriented pyrolytic graphite (HOPG) has a very high thermal conductivity over four times that of copper. However, it is expensive, it is a soft material, like mica, that is difficult to machine, it is not readily susceptible to electrical discharge machining (EDM), and it has been perceived as difficult to reliably braze. In addition, pyrolytic graphite is highly anisotropic. The physical properties vary widely, dependent on the chosen plane of its hexagonal crystal structure. It would thus be advantageous to demonstrate methods by which HOPG can be employed to manufacture reliable and high-performance microwave components that overcome the disadvantages of the prior art.